The present invention relates generally to the field of medical devices and measurements. More particularly, the present invention relates to a method and apparatus for measuring cervical dilation of a patient during pregnancy and labor.
The uterine cervical canal serves as the conduit for the human fetus to exit the uterus and subsequently pass through the vagina during the birthing process. It has long been known that the cervix normally undergoes a series of physical and biochemical changes during the latter portions of pregnancy which enhance the ease and safety of the birthing process for the mother and the infant. For example, in the early stages of labor the tissues of the cervical canal soften and become more pliable, the cervix shortens, and the diameter of the cervical canal begins to increase at its proximal end at the internal os. As labor progresses, the cervical diameter growth propagates to the distal end of the cervical canal to the external os. In the final stages of labor, the external Os dilates allowing for the unobstructed passage of the fetus.
The monitoring of cervical diameter via serial vaginal exams is critically important in labor management. This information regarding the progress of labor is used to diagnose such conditions as dysfunctional or arrested labor and cephalopelvic disproportion, determine the necessity for labor augmentation or cesarean section, indicate when the patient should begin to push the baby out, and determine the appropriateness and timing of administering various anesthetic/analgesic agents, among other things. The vaginal exam is performed by inserting the first and second fingers of a gloved hand into the vagina and up to the cervix. By spreading the two fingers across what is perceived to be the internal diameter of the cervix, an assessment is made, based on experience, about the cervical dilatation in centimeters.
Obstetricians, and other health care providers that are certified to attend obstetrical patients (family practitioners, nurses, midwives), are usually well practiced in the art of manual, digital cervical diameter measurement. An individual practitioner can achieve acceptable repeatability using this method. However, the variation between providers is known to be quite significant due to the subjective nature of the measurements. In addition, such measurements are discrete and must be performed serially to assess labor progress and ascertain whether interventions-are required. It is not an efficient use of a busy obstetrician's time to perform these serial exams, especially when he/she is attending to multiple laboring patients, some percentage of whom may have complications that require most of his/her time.
Despite the use of gloves, vaginal exams also carry with them the risk of causing infections of the fetal membranes (chorioamnionitis), the lining and/or muscle of the uterus (endomyometritis), or of the infant (neonatal sepsis). The risk increases dramatically once the fetal membranes have been ruptured and is related to the number of vaginal exams, among other factors. For this reason, the number of vaginal exams must be kept to a minimum after the membranes have been ruptured.
The measurement of cervical dilatation is also important in patients at risk for preterm labor (prior to 37-38 weeks gestation depending on definition). Neonatal morbidity and mortality increases with the degree of prematurity, so early diagnosis of preterm cervical dilatation and expeditious intervention is critical.
Given the above, it is not surprising that there have been numerous historical attempts to: (A) Provide a more accurate user-independent cervical diameter monitoring device and/or (B) Provide an automatic cervical diameter measuring device. We will review several of these historical attempts below.
Unfortunately, none of these prior-art devices are practical for everyday, inexpensive use for one or more reasons. Consequently, there is currently no commercially available, objective monitoring system for cervical diameter, and the measurement of cervical diameter continues to be performed solely by manual, digital examination.
Reasons for failure of prior-art devices to gain acceptance include:
1) Patient discomfort and cervical tissue trauma due to attachment means.
2) Lack of accuracy due to: (a) imposed cervical tissue distortions, (b) inherently inaccurate sensors, (c) unpredictable sensor reorientation (twisting) errors, (d) flaws in assumptions (ultrasonic cervimeters) and (e) lack of proven and published correlations between other measured cervical-tissue parameters and the actual desired cervical diameter.
3) Blockage of the cervical canal (thus inhibiting other manipulations including the insertion and operation of fetal or intrauterine probes.
4) Complexity of installation.
5) Lack of disposability (thus high cost and a need to resterilize the device).
6) Electrical shock hazards.
7) Unsuitable for ambulatory and/or at-home use.
It would therefore be desirable to provide improved devices and methods for measuring cervical diameter and dilation which overcome at least some of the shortcomings listed above. It would be particularly desirable, at least for patients in danger of premature delivery, if cervical diameter could be measured and monitored at home and, ideally, in an ambulatory manner.